Yeah, I don't think that GIMP really allows for PAT files, which are what Photoshop patterns are. You can use Photoshop BRUSHES in GIMP, but I don't think you can use patterns.
I could be wrong, but that's what I"ve heard - so that's why I list these as Photoshop only.
However, this set just happens to have an image pack that you can grab for it, which are the JPGs I use to make the patterns. Follow the link in the description for the licenses, and there'll be a download link below the regular download link. You're looking for the image pack.
Hope this helps!